The present invention relates generally to medical devices and, in particular, aortic cannulas. Aortic cannulas are used to return blood to the aorta while the heart is by-passed during heart surgery. These cannulas are purposely made with small diameters to minimize the disruption to the aorta, which in many heart surgery patients have advanced complex atherosclerotic plaque with adherent blood thrombi.
Aortic cannulas generally comprise an elongated tube having a terminal end. In at least some styles of conventional cannulas, a single opening is provided in the terminal end which provides a single stream of blood exiting the cannula and entering the aortic arch. Due to the small diameter of the cannula, the flow velocity of the blood through the single opening in the terminal end of the cannula is extremely high, resulting in xe2x80x9cjetxe2x80x9d flow. The fluid pressure at the discharge end of the prior art cannula is also high. It is believed that the force of this jet stream of blood dislodges atherosclerotic plaque and/or adherent thrombi from the walls of the aorta, causing embolisms and strokes.
Attempts in the art to prevent embolisms resulting from cannulation have included designing the cannula in order to reduce the velocity of blood exiting the terminal end. For instance, U.S. Pat. No. 5,354,288 describes a cannula having a conical diffuser placed toward the proximal end of the cannula. The cannula includes several outlet openings in the sidewall to permit blood deflected by the diffuser to flow out of the cannula. This cannula design, however, still directs blood toward the sides of the aortic arch wherein the atherosclerotic plaque usually lies. Thus, the patient is still susceptible to embolisms and strokes.
Therefore, a primary objective of the present invention is the provision of an aortic cannula which does not cause injury to the aortic tissues or dislodge atherosclerotic plaque during cannulation.
Another objective of the present invention is the provision of an aortic cannula which reduces the velocity of the blood exiting the cannula.
A further objective of the present invention is the provision of an aortic cannula which reduces the risk of embolisms or stroke present with the use of conventional cannulas.
Yet another objective of the present invention is the provision of a aortic cannula which is economical to manufacture and convenient, durable, and safe to use.
These and other objectives will be apparent from the following description of the invention.
The improved aortic cannula of the present invention includes an elongated tube having a terminal end. The improvement comprises two large openings adjacent the terminal end of the cannula as well as an inverted cup at the terminal end of the cannula. The openings at the terminal end reduce the velocity of the exiting blood and the inverted cup redirects the flow of blood as it exits through the discharge openings. The blood jet exits in a rearward direction towards the ascending aorta, and away from the aortic arch, which often contains atherosclerotic plaque. Thus, the risk of stroke from dislodged plaque is significantly reduced.